<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>10.TODO任务列表中使用WeakSet</title>
  <style>
      * {
    padding: 0;
    margin: 0;
  }
  body {
    padding: 200px;
  }
  ul {
    list-style: none;
    display: flex;
    width: 200px;
    flex-direction: column;
  }
  li {
    height: 30px;
    border: solid 2px #e67e22;
    margin-bottom: 10px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-left: 10px;
    color: #333;
    transition: 1s;
  }
  a {
    border-radius: 3px;
    width: 20px;
    height: 20px;
    text-decoration: none;
    text-align: center;
    background: #16a085;
    color: white;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    margin-right: 5px;
  }
  .remove {
    border: solid 2px #eee;
    opacity: 0.8;
    color: #eee;
  }
  .remove a {
    background: #eee;
  }
  </style>
</head>
<body>
    <ul>
      <li>houdunren.com <a href="javascript:;">x</a></li>
      <li>hdcms.com <a href="javascript:;">x</a></li>
      <li>houdunwang.com <a href="javascript:;">x</a></li>
    </ul>
    <script>
      class Todos {
          constructor() { }
          run () {
            this.items = document.querySelectorAll("ul>li");
            this.lists = new WeakSet();
            this.record();
            this.addEvent();
          }
          addEvent () {
            this.items.forEach(item => {
              item.querySelector("a").addEventListener("click", event => {
                //检测WakeSet中是否存在Li元素
                const parentElement = event.target.parentElement;
                if (!this.lists.has(parentElement)) {
                  alert("已经删除此TODO");
                } else {
                  //删除后从记录的WakeSet中移除
                  parentElement.classList.add("remove");
                  this.lists.delete(parentElement);
                }
              });
            });
          }
          record () {
            this.items.forEach(item => this.lists.add(item));
          }
        }
        new Todos().run();
    </script>
</body>
</html>